Alternatively activated RAW264.7 macrophages enhance tumor lymphangiogenesis in mouse lung adenocarcinoma

Abstract

Tumor-associated macrophages (TAMs) have been implicated in promoting tumor progression and invasion. The onset and maintenance of tumor angiogenesis and lymphangiogenesis also seem to be partly driven by a group of polarized alternatively activated macrophages (aaMphi) in lung adenocarcinoma. Here, the aaMphi and classically activated macrophages (caMphi) were obtained using RAW264.7 cells via IL-4 and IFN-gamma + LPS treatment, respectively. Co-inoculation of aaMphi with Lewis lung carcinoma (LLC) cells promoted tumor growth, increased lymph node metastasis, and reduced the survival in C57BL/6 mice bearing LLC. Furthermore, the effects of the activated macrophages on the lymphangiogenesis-related properties of lymphatic endothelial cells (LECs) were investigated in vitro. When LECs were cultured in macrophages conditioned medium or in a co-culture system of macrophages and LECs, aaMphi significantly promoted proliferation, migration, and tube-like formation of LECs. We identified high VEGF-C expression in aaMphi and low expression in caMphi as well as unactivated macrophages by ELISA and Western blotting. In LECs, co-culture with aaMphi resulted in a significant increase of mRNA levels of specific lymphatic marker VEGF receptor-3 and the homeobox gene Prox-1, as well as lymphangiogenic factor VEGF-C rather than VEGF-D by quantitative RT-PCR. Furthermore, enhanced LECs migration and capillary formation by co-culture with aaMphi were significantly inhibited by rVEGF receptor-3/Fc chimera. In conclusion, these data show that aaMphi play a critical role in tumor-induced lymphangiogenesis through up-regulating VEGF-C and increasing lymphangiogenesis-related behavior of LECs, which may contribute to lymphatic invasion in lung adenocarcinoma.

Tumor-associated macrophages infiltration is associated with peritumoral lymphangiogenesis and poor prognosis in lung adenocarcinoma

“…Recently, Mantovani et al found that TAMs might be polarized toward an aaMphi phenotype [22]. In our previous study, we reported that alternatively activated TAMs can induce peritumoral lymphangiogenesis in mouse Lewis lung adenocarcinoma [16]. Briefly, coinoculation of aaMphi with Lewis lung carcinoma (LLC) cells promoted tumor growth, increased lymph node metastasis and reduced the survival in C57BL/6 mice bearing LLC.…”

“…Schoppmann et al reported that the peritumoral inflammatory reaction and vascular endothelial growth factor (VEGF)-C expressing TAMs increase tumor lymphangiogenesis and lymphovascular invasion in cervical cancer [14] and invasive breast cancer [15]. Recently, we reported that similar to TAMs, alternatively activated macrophages have a potent effect on the lymphangiogenesis-related properties of lymphatic endothelial cells (LECs) though up-regulating VEGF-C expression and secretion [16]. However, in lung adenocarcinoma, the correlation between TAMs infiltration and peritumoral lymphangiogenesis remains unknown.…”

IGFBP7 functions as a potential lymphangiogenesis inducer in non-small cell lung carcinoma

“…Formation of tube-like structures was monitored by microscopic observation at a magnification of x100 over 6 different fields of each well. They were then photographed to measure the length of tube-like structures as previously described (19).…”

Fra-1 protooncogene regulates IL-6 expression in macrophages and promotes the generation of M2d macrophages

“…As the major inflammatory component of the stroma of many tumors, tumor-associated macrophages (TAMs) can affect different aspects of the neoplastic tissue [1,5]. Recent experimental studies indicate that TAMs play a detrimental protumor role in the initiation of tumorigenesis, promotion of angiogenesis and lymphangiogenesis, growth, invasion and metastasis of tumor cells and the suppression of adaptive immunity [1,[5][6][7][8]. Clinical studies have shown that a high density of these TAMs correlates with a poor prognosis in over 80% of studies published, such as those in breast, prostate, cervical and ovarian cancers [9].…”